Third Generation Partnership Project (3GPP) Fifth Generation (5G) wireless communication systems are being developed. Evolving 5G networks play a critical role to keep up with increasing demands for connectivity. In order to support the increased traffic demands and data throughput, 5G will extend the range of carrier frequencies to millimeter waves.
Devices supporting 5G (e.g. a user equipment (UE)) includes baseband (BB) circuitry (e.g. a baseband integrated circuit (IC) chip) and radio frequency (RF) circuitry (e.g. an RF IC chip). The RF circuitry is placed near the antenna (e.g. active antenna) of the device.
Interfacing between the baseband IC and the RF IC in a millimeter wave frequency instead of low intermediate frequency (IF) avoids the need for IF to RF conversion in the RF IC and vice versa. It provides various benefits for co-running with sub-7 GHz communication systems as well as regulatory conformance. However, this RF architecture can be sensitive to stability and oscillation since input and output frequencies to and from the RF IC are the same. In this case, when the leakage level from the antennas to the RF IC interfaces (towards the BB IC) is close to, or lower than, the gain of the RF IC (either in Rx or Tx) then the amplifiers within the RF IC will have positive feedback and become unstable. These strong leakages are very common and are difficult to mitigate with hardware solutions due to the small form factor of the antenna modules, the beamforming effect allowing for all leakages to combine coherently, and the nature of the millimeter wave frequencies.